Nickel Zinc rechargeable batteries are not common, however HobbyKing sell them. I decided to get a batch and have a look at them in the KX1.
NiZn batteries are not for everyone. Firstly, the capacity is lower at 1500mAh than the typical NiMH battery at 2400mAh. The plus side is that the NiZN carry a higher voltage. It is at 1.85V at the top of the cycle and then slowly decreases throughout the cycle, but remaining well above NiMH, and even Alkaline batteries that start at just under 1.6V and decline to 1.1V over the cycle. NiMH spend most of their cycle flat at 1.2V.
For a radio like a FT-817 that linearly regulates the voltage, there is no point using AA cells with higher voltage, as the regulator literally burns the excess voltage as heat. The 1.2V of NiMH are fine in that application. The KX1 is a different matter.
The KX1 has a capacity for 6 internal AA cells. Using NiMH cells, these would deliver only about 7.2V for most of the cycle, which is below the recommended minimum voltage required by Elecraft. The rig still works – although I have not extensively tested it. The power levels generated are very low – perhaps only good for QRPp levels of 500mW or less. I am quite happy with QRP operating, but I don’t see a pressing need to go to QRPp at this stage.
The NiZn cells represent an opportunity to mix things up with a higher voltage that the KX1 can then use to generate more RF power. It won’t give me more operating time, but it will give me more punch. Here’s a look at 6 NiZn cells installed inside the KX1 AA battery holder:
The cells come charged, and showed 1.85V per cell and a total of 11.1V installed. I used the cells for several hours in the field, and I came back with the six cells developing 10.4V across them. The KX1 would develop low 1W to 2.5W depending on the band and (reasonable) antenna configuration. This was only a little down from what power it was developing with a 12.2V external supply.
The 1500mAh capacity would mean that these NiZn cells will deliver many hours, perhaps more than 20 hours, of operating time in the field. The low RX current draw of the KX1 is certainly a great factor here, especially compared to a all mode rig like the FT-817. This kind of setup would be really useful for multiday remote area activations, where the radio part of the gear needs to be kept to an absolute minimum for weight reasons – for example when South West Tasmania or Fiordland in New Zealand are part of the Summits on the Air program.
Regards, Wayne VK3WAM